1. Field of the Invention
This invention relates generally to an apparatus for placing a band around an object, and more specifically to an apparatus for properly opening, shaping, orienting and positioning a band of shrinkable film as it is placed about a container.
2. Description of the Prior Art
The food, drug and cosmetics industries are becoming increasingly concerned with the possibility that unscrupulous persons may be able to tamper with products before they have been distributed to consumers. In many instances, tamperers open sealed containers, add injurious substances to these containers, reseal them, and replace them for eventual public consumption. Frequently, the tamperers obtain the product by buying it from retailers, and after the product has been adulterated, the tamperers surreptitiously replace the product on the retailers, shelves. To improve consumer safety, manufacturers and packagers now shrink a band of thin plastic film around the necks of their containers. This is commonly known as the "tamper-evident" seal. A would-be tamperer will be unable to open a sealed container without destroying the film seal. Even if the tamperer cuts the band from the container and glues it back on, there will be a fine line where the band was cut. A consumer therefore has an aid in determining whether the container he is considering buying has been unsealed by making sure that the band of film surrounding the cover opening is present and intact. Absence or mutilation of this band is an indication of possible product tampering and consumers are warned, usually on the container's packaging, not to use the material in any container which has a missing or mutilated band.
Today, tamper-evident seals are made by placing a somewhat oversize band of film around the region where a container and container top meet. These film bands are preferably made from heat-shrinkable polymers such as polyethylene or polyvinyl chloride. When placed around the container, the band is somewhat larger than the container. Once properly positioned around the container, the band is heated and shrinks to form a tight seal around the container's closure.
Many devices are known for placing bands of film around containers. Some such devices are disclosed in U.S. Pat. Nos.: 4,562,684; 4,286,421; 4,293,364; 4,184,309; 2,890,558 and 2,103,302. Most of these devices grab preformed bands of shrinkable film in vacuum suction jaws, and then move the jaws so that the band is properly placed about the container. These jaws only grip bands when connected to a vacuum; to release the bands, all that need be done is interrupt the vacuum.
The extent to which known heat-shrinkable films can be made to contract with aesthetic neatness upon heating is not all that great. This behavior means that the unshrunk film bands cannot be all that much larger than the container necks. Should the bands be made too large, then during heating they may not shrink enough to form a tight seal around the container. At the same time, if the bands are too close in size to the containers, there will be very little clearance between them and this may complicate band positioning. One reason to use unshrunk bands that are only slightly larger than the container being sealed is that only a slight amount of shrinkage will be needed to bring the band into contact with the container, and additional shrinkage will simply produce a very tight aesthetically neat seal that is very difficult to remove. Because in practice the clearance between unshrunk band and the container closure is not all that great, the bands have to be properly opened and shaped as they are positioned around containers. If the bands are not properly opened and shaped, they may brush against the containers as they move downward onto the containers. This may cause the bands to be misoriented on the containers. In addition, the mispositioned bands may jam between the vacuum jaws and the container, forcing the sealing machine operator to stop the banding machine so that he can clear the jam. Since a failure to properly open and shape shrinkable bands can result in poor product appearance or decreased production levels, there is a real need to keep the bands properly opened and shaped during placement.
Early band applicators carried pre-cut bands in magazines. One such device is disclosed in U.S. Pat. No. 2,103,302. The sealing machine disclosed in U.S. Pat. No. 2,103,302 employed several individual linear sealing assemblies arranged in series. Containers to be sealed moved past these sealing assemblies. A number of sealing assemblies were used, presumably because a single assembly was not capable of operating at a sufficient speed. By using more than one sealing assembly, machine output could be increased in direct proportion to the number of additional sealing assemblies.
In time, banders having band placement equipment mounted on rotary turrets were introduced. These devices were able to achieve increased banding rates because they moved the band placement equipment along with the moving containers. Such devices are disclosed in U.S. Pat. Nos. 2,890,558, 4,184,309, 4,293,364 and 4,562,684.
In order to make efficient use of packaging equipment, it is necessary to maximize the number of containers banded for a given period of time. In other words, it is desirable to operate the machinery at as high a speed as possible. At the same time, the machine cannot be run so fast as to cause machine failures, which these result in unproductive down-time when the equipment is idled for repairs.
One device for applying bands of shrinkable film to containers is disclosed in U.S. Pat. No. 4,562,684 the disclosure of which is incorporated herein by reference. This device carries several band positioning assemblies on a vertical rotary turret having a horizontal axis of rotation. Bands of film are grasped, opened and positioned around moving containers, all while moving around the horizontal axis. The bands are grasped by a pair of vacuum jaws which rotate with the turret. The bands are oriented so that once held in the vacuum jaws they continue to rotate downward until they are positioned around the container. The bands are released by interrupting the vacuum holding them in the jaws when the bands fully encircle the container necks.
The higher the speed at which banders operate, the more likely they are to experience band misorientation or jamming. At high banding rates, the collapsed bands have little time to open. Furthermore, the rapid movement of the bands from the grasping position to the placement position creates air drag, causing the opening band to buckle or bend.
It is always desirable to raise the banding rate; however, as this rate is increased, band positioning accuracy will ultimately decrease until the incidence of mispositioned or jammed bands becomes unacceptable. Thus, there exists a genuine need to improve band opening and shaping and the accuracy with which the bands are positioned regardless of the rate of banding.